An Investigation of Stucco Wall Assembly Performance by Hygrothermal Simulation

Stucco walls are widely used, traditional building assemblies that have persisted by evolving to meet changing design criteria. In North America, stucco is a popular cladding choice both for its aesthetic appearance and for its inherent fire-resistant properties. Stucco use has increased in U.S. residential construction, comprising 27% of the U.S. primary exterior wall material in 2019, up from 16% 25 years earlier. Despite stucco's popularity, stucco systems have been associated with several performance questions, including cracking and water intrusion. These documented issues have spurred code and standard activity and product development over the last two decades. This study uses hygrothermal analysis to investigate several possible water intrusion mechanisms in stucco wall assemblies, including water absorption followed by inward vapor drive, water intrusion through stucco cracks, and bulk water intrusion at junctions or interfaces (e.g., window-wall interfaces). The analysis includes the relative severity of the moisture intrusion mechanism as a function of climate and assembly design. The assemblies considered were chosen considering recent and upcoming code and standard changes, including the addition of drainage and ventilation behind the stucco cladding. The efficacy of behind-cavity drainage and ventilation for mitigation of water intrusion mechanisms is analyzed.